(1) Field of the Invention
This invention relates to a novel method for producing alkylstyrenes. Furthermore, the invention relates to a method for producing alkylstyrenes by catalytically cracking 1,2-di(substituted phenyl)ethane in the presence of an acid catalyst.
More particularly, for example, 4-isobutylstyrene is prepared by catalytically cracking 1,2-di(4-isobutylphenyl)ethane. This 4-isobutylstyrene can be used for preparing .alpha.-(4-isobutylphenyl)propionic acid (tradename: "ibuprofen") which is useful as a medicine for the relief of pain and inflammation.
(2) Description of Prior Art
The alkylstyrene is a material which is useful as a comonomer for improving weather-proofness of synthetic plastics and as an intermediate in the organic chemical industry. In order to produce this useful alkylstyrene, there have been proposed several methods as follows in which 1,1-di(substituted phenyl)ethane is cracked in the presence of an acid catalyst.
Ind. Eng. Chem., Vol. 46, No. 4, 652 (1954) PA0 J. Chem. Eng. Data, Vol. 9, No. 1, 104 (1964) PA0 I. & E. C. Prod. Res. Dev., Vol 3, No. 1, 16 (1964)
In the above references, it is disclosed that methylstyrene and dimethylstyrene are obtained by cracking 1,1-ditolylethane and 1,1-dixylylethane, respectively. Furthermore, ethylstyrene, isopropylstyrene and tertbutylstyrene are also referred to.
There are other references which disclose more particular methods:
In U.S. Pat. No. 2,420,689 is described a method for producing dimethylstyrene by cracking 1,1-dixylylethane in the presence of a kaolin catalyst.
In U.S. Pat. No. 2,422,318 is described a method for cracking asymmetrical 1,1-diarylethane.
In U.S. Pat. No. 2,864,872 is described a method to use silica as a cracking catalyst.
In U.S. Pat. No. 2,954,413 is described a method for cracking 1,1-dixylylethane in the presence of a fluidized catalyst.
In U.S. Pat. No. 3,025,330 is described a method for producing methylstyrene from 1,1-ditolylethane.
In U.S. Pat. Nos. 2,976,333 and 2,976,334 are described methods for improving the catalysts for cracking.
Furthermore, in U.S. Pat. No. 4,694,100, it is described that 1,1-di(4-isobutylphenyl)ethane is catalytically cracked to prepare 4-isobutylstyrene. According to this reference, the 4-isobutylstyrene is then carbonylated to produce ibuprofen.
In the methods for cracking 1,1-di(substituted phenyl)ethane as disclosed in the above references, not all of the 1,1-di(substituted phenyl)ethane is cracked and converted into alkylstyrene and alkylbenzene, and it cannot be avoided that unreacted 1,1-di(substituted phenyl)ethane remains in the reaction mixture as a matter of course. This is apparent from the fact that the purpose conversion rates in the methods proposed in the above references are from 40% to 60%.
In order to produce economically alkylstyrene by cracking 1,1-di(substituted phenyl)ethane, the reuse of the unreacted 1,1-di(substituted phenyl)ethane is inevitable. That is, it is an inevitable condition for industrially economize the cracking reaction that the fraction mainly containing 1,1-di(substituted phenyl)ethane that is separated from a reaction mixture is used again for a cracking step.
The inventors of the present invention have made extensive investigation with regard to the preparation of alkylstyrene by cracking. As a result, it was found out that the cracking of the fraction as it stands which mainly contains unreacted 1,1-di(substituted phenyl)ethane recovered from the cracking processes of said compound, is undesirable, and in order to solve this problem, the present invention has been accomplished.
That is, in the cracking of 1,1-di(substituted phenyl)ethane in the conventional art, substituted ethylene components which are formed by dehydrogenation caused by a cracking catalyst are contained in the unreacted 1,1-di(substituted phenyl)ethane fraction as shown by the following chemical equation. When the cracking of such material of the unreacted 1,1-di(substituted phenyl)ethane fraction containing the substituted ethylene components is carried out, the life of cracking catalyst is affected undesirably. Of course, it is not economical to separate the substituted ethylene components by an industrial separation method such as distillation because the boiling points of the components are close. EQU Ar--CH(--CH.sub.3)--Ar.fwdarw.Ar--C(.dbd.CH.sub.2)--Ar
wherein Ar is an aryl group.
Accordingly, the method for producing alkylstyrene by cracking 1,1-di(substituted phenyl)ethane is not desirable and the improvement in the method has been sought.
Furthermore, other than the above catalytic cracking, the simple thermal cracking without using any catalyst is not desirable because various components as well as the substituted ethylene components and even polymeric substances are produced together.